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# Motor effect - help! Watch

1. Hi everyone!

I've been learning about the motor effect in GCSE physics.

I've finally managed to grasp some understanding on how a commutator works, and how current in the coil is reversed twice at every turn (of 360 degrees) . However, in my book it says that "the current direction in the coil is reversed twice every turn - changing the direction of the magnetic forces". <-------This bit I don't understand.

Why do the magnetic forces produced by the fixed magnets need to change, if the current is reversed for each end of the coil doesn't the forces act in the same direction?

2. (Original post by park1996)
Hi everyone!

I've been learning about the motor effect in GCSE physics.

I've finally managed to grasp some understanding on how a commutator works, and how current in the coil is reversed twice at every turn (of 360 degrees) . However, in my book it says that "the current direction in the coil is reversed twice every turn - changing the direction of the magnetic forces". <-------This bit I don't understand.

Why do the magnetic forces produced by the fixed magnets need to change, if the current is reversed for each end of the coil doesn't the forces act in the same direction?

You've heard of Fleming's hand rules, right? For a motor, you use Fleming's right hand rule. Hold out your right hand; taking the middle finger as the current and the thumb as the force/motion, doesn't that change when you change the direction of the current? The fact that the motion/force is changing is the reason why the motor rotates. The magnetic field remains constant, I think what they mean by the magnetic force is the motion of the motor.
3. (Original post by You-know-who)
You've heard of Fleming's hand rules, right? For a motor, you use Fleming's right hand rule. Hold out your right hand; taking the middle finger as the current and the thumb as the force/motion, doesn't that change when you change the direction of the current? The fact that the motion/force is changing is the reason why the motor rotates. The magnetic field remains constant, I think what they mean by the magnetic force is the motion of the motor.

Thank you so much - you cleared up so much for me!!

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Updated: April 3, 2013
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